In a parking lot, the first row can hold (20) cars and each next row can hold (4) more cars. What is the total capacity of (7) rows?

Correct answer: 224

The row capacities form an AP: \(20,24,28,\ldots\), where \(a=20\), \(d=4\), and \(n=7\). Thus, \(S_7=\frac{7}{2}[2(20)+(7-1)4]=\frac{7}{2}(64)=224\). Therefore, the total capacity is 224 cars. A value such as 232 can result from using an incorrect last term. Exam tip: In AP word problems, identify \(a\), \(d\), and \(n\) before applying the sum formula.